Except, of course, that it won't.
If you were ever capable of believing that a man already set on murder, as was, evidently, Muhammad Youssef Abdulazeez, would be deterred by a sign, then I think we have to admit to ourselves that while you are capable of believing anything, you are capable of learning nothing.
If you ever endorsed the efficacy of the "gun free zone," that means you were possessed of the sort of spectacularly limber imagination that George Lucas or Walt Disney could only envy. Because you were able to picture, in your mind's eye, a disgruntled ex-employee or a seething jihadi or a garden variety madman -- heedless of the laws of God and man that have ever prohibited murder -- being pulled up short by silhouette of a gun and null sign. You could script an internal conversation that went something like this:
"Well. I had planned on annihilating everyone in the place, before sending myself to join them in hell or paradise. But whereas I don't care how many of my fellow men have to die to (satiate my rage) (satisfy my theology) (silence the voices in my head), I am certainly not going to stoop to taking a gun into a building that is quite clearly labeled to bar such conduct.
Why, that would be wrong.
I suppose I'll just go home."
A mind that can contain that depth of imagination has its merits, but it's not the sort place terribly hospitable to facts.
If you ever argued that "gun free zones" make anyone safer from anything or anyone, then you are either a hoplophobic fool or -- and this, I fear, is too widely the case -- the sort of heartless ideologue for whom truth is a mere speed bump on the way to the tyranny you desire, and for whom today's events in Chattanooga are nothing more nor less than another crisis not to be wasted.
As I have said and said and said - Robert's Rule holds that gun free zones aren't.
But then you knew that, didn't you?